High speed electronic control of fluid flow using inexpensive batch fabricated valve arrays is potentially critical for numerous applications, including distributed actuator controls, paper or object positioning, dynamic control of fluid instabilities, or microcontrol of microchemical reactions and biological assays. Other potential applications include use of valves to drive physical elements that support tactile displays or other virtual reality interface tools. However, large two dimensional arrays of microvalves (e.g. 100.times.100 valves or more) can be difficult and expensive to construct to the necessary tolerances, and reliable addressing of specific valves to open or close on a millisecond time scale is often not feasible.
The present invention provides a novel valve capable of being arranged in two dimensional valve arrays allowing millisecond time response and high throughput of the aggregate array and the ability to control flow with large pressure differentials. Moreover each valve in the array is capable of control by passive or active matrix addressing. In a preferred embodiment, each valve includes a valve housing having an aperture plate defining an aperture therethrough, and an opposing plate positioned in spaced apart relationship to the aperture plate. A flexible electrically conductive film or strip is attached at its first end to the aperture or opposing plate and is free to move between the plates at its second end. Valve action is provided by use of at least one switching electrode for moving the flexible film between an aperture open position and an aperture blocking position. A dielectric layer between the flexible conductive film and the switching electrode prevents shorting.
In preferred embodiments, various valve modifications can be employed to enhance valve operation, minimize power requirements, and increase valve switching times. For example, instead of a circular or elliptical aperture cross section, the aperture can be defined to have at least one acute vertex, providing a point release for air inflow or outflow. The flexible film does not have to be a straight, homogenous strip, but can be varied in composition, width, thickness, and stiffness along its length. In other configurations, electrode size, positioning, and geometry can be varied. Electrode modifications, and other mechanical modifications to the flexible film, allow for tuning valve response time, decreasing or increasing valve pressure strengths, and varying electrostatic interactions.
Advantageously, valves of the present invention can be arranged into large passively addressable arrays. Such arrays include a plurality of valves, with each valve defining an aperture therethrough, and a plurality of flexible films respectively attached to each of the plurality of valves, with each flexible film independently addressable to alternately switch between an aperture blocking position and an aperture open position. A switching voltage source is used to maintain a subset of the plurality of valves at either a non-switching voltage or a switching voltage. When switching electrodes are activated for applying an electrostatic switching force to move the plurality of flexible films, only that subset of the plurality of valves having flexible films maintained at the switch voltage transition between the aperture blocking position and an aperture open position. In practice, usually two address lines connected to each valve in a valve array are required. Opposing switching electrodes are respectively addressed at one of two possible voltage differences, high (e.g. positive or negative 100 volts) or low (0 volts). To switch the film from a blocking to a non-blocking position, or vice versa, it is necessary to switch the voltages. In the non-blocking voltage state fluid pressure forces the free end of the flexible strip away from the blocking position. When a particular valve in a two dimensional row and column array is to be switched, the voltage difference applied to all flexible strips in a particular row (or column) is changed from an intermediate voltage (e.g. 50 volts) to a switching voltage. Ordinarily, only that valve at the intersection of the row (or column) and column (or row) of opposing electrodes actually switches, with the others valves addressed in the array remaining unchanged. Of course, by appropriate row and column multiplexing, multiple switching in parallel is possible.
In a preferred embodiment, the use of independently addressable valves allows for high spatial precision transport of objects, including flexible objects such as paper. For certain applications, including processing of high purity or delicate materials, contamination or damage to the object may result from mechanical grasping or contact. This is particularly true for high speed processing systems, which may damage objects simply by engaging them. For example, high speed rollers may damage paper through differential engagement of misaligned paper with the roller, resulting in ripping or tearing of the paper. Fortunately, mechanical or frictional engagement is only one possible means for moving an object. Object drive mechanisms based on various fluid support techniques have long been employed to move delicate objects without requiring solid mechanical contact. For example, instead of using conventional belts, conveyors or rollers, paper moving through xerographic copier systems can be supported on a laminar air flow, or uplifted and moved by valve controlled air jets. This is particularly advantageous, for example, when sheets of paper carrying unfixed toner images must be moved between a photoconductive drum and a fusing station where the toner image is fixed. With conventional physical rollers, the continuing possibility of dynamic distortions to the toner image, or even slight misalignments resulting in image degradation, must always be considered.
Accordingly, the present invention provides a fluid transport apparatus and method for moving a flexible object that does not require physical contact. The present invention can effectively work with either continuous or discrete flexible objects moving through a materials processing system. A fluid pressure source is connected to a plurality of valves, with each valve defining an aperture therethrough, and having a plurality of flexible films respectively attached, with each flexible film independently addressable to alternately switch between an aperture blocking position and an aperture open position.
An S-wave valve is described in U.S. Ser. No. 08/711,229, "Passively Addressable Fluid Valves Having S-Shaped Blocking Films", is assigned to the same assignee as the present invention and is hereby incorporated by reference. The S-Wave valve structure requires a flexible membrane which spans from the bottom to top of a rectangular shaped cavity, or cavity with a topologically similar cross section. The length of the membrane must therefore be longer than the diagonal of the rectangle. Controlling the extra length in a batch fabrication process is difficult. The S-wave valve also utilizes two actuation electrodes, a top and a bottom electrode. A cantilever valve structure for closure of a pressurized air stream needs only one electrode and can be fabricated using a simpler planar technology. Furthermore, length control is not an issue. The cantilever structure maintains the high conductance of the full S-wave and shares the minimal electrostatic gap of both S-wave and cantilever valves.
Additional functions, objects, advantages, and features of the present invention will become apparent from consideration of the following description and drawings of preferred embodiments.